Boating communities may sometimes have marina pools so that residents may keep their vessels in the water. These marina pools are generally constructed adjacent a navigable waterway. Further, a barrier generally separates the marina pool from the adjacent navigable waterway. There are many advantages to marina pools, such as a more protected environment for keeping a vessel in water, for example.
One disadvantage that exists with boating communities that have such marina pools, however, is that in order for the vessel to be used in the adjacent navigable waterway, it must first be transferred from the marina pool to the navigable waterway. More particularly, the marina pool may have a first water level, and the navigable waterway may have a second water level.
U.S. Pat. No. 5,947,639 to Bishop et al. discloses a boat lift apparatus for lifting a boat out of water to thereafter transfer the boat over a barrier that separates a first body of water from a second body of water. The boat lift apparatus includes a carriage connected to a pair of opposing horizontal supports. The carriage includes a plurality of slings that extend downwardly, and that may be moved between a lowered position and an elevated position. When in the lowered position, the slings may engage the hull of the boat so that when the slings are elevated, the boat is lifted out of the water. When the boat is lifted out of the water, the carriage may be moved in a horizontal direction to thereby transfer the boat over the barrier.
U.S. Pat. No. 6,457,904 also to Bishop et al. discloses a boat lift apparatus including a vertically movable lift frame support bed which rolls on tracks that are positioned adjacent a barrier separating a first body of water from a second body of water. Both of the Bishop et al. patents require that the vessel be raised completely out of the water.
U.S. Pat. No. 423,561 to Jebens discloses a floating lock for use in canals to move a vessel from one water level to another. The floating lock includes a tank that is movable between elevated and lowered positions. The floating lock also includes a watertight drum positioned in a well, and a cylinder for lifting the tank connected to the watertight drum. As the tank is lowered, the cylinder fills with water, and as the tank is raised, water in the cylinder drains into the well. Displacement of the watertight drum is overcome by the weight in the cylinder to lower the tank. This system, however, may be quite expensive and complicated to install, as well as time consuming to construct. Further, using such a system to transfer a vessel from one water level to another may be very slow.
U.S. Pat. No. 802,576 to Lohle et al. discloses a boat lift apparatus including a tank having a rotating carriage that engages a large screw-thread to move the tank between elevated and lowered positions. The tank is suspended from vertical posts that extend above the sidewalls of the tank, out of the water. Again, this system may be very expensive, complicated, and time consuming to install, and may also be slow to transfer a vessel between two bodies of water.